The Penobscot River estuary winter eagle population is derived strictly from 

 seasonal immigration. Winter occupancy levels there vary more than those of 

 other coastal regions, where resident eagles may remain throughout the year. 

 The Kennebec River estuary is notable for high proportion of immature eagles 

 among its wintering eagle populations. The 1977 to 1979 mean was 45%. This 

 fact is significant in view of the nearly complete nesting failure of eagles 

 nesting in the Kennebec River watershed. It confirms the probability of a 

 seasonal influx of nonresident eagles into coastal regions where resident 

 breeding populations may also winter. 



The composition of coastal Maine's 1977 to 1979 midwinter eagle populations by 

 age class averaged 83% adult and 17% immature eagles. Previous counts of 

 eagles wintering in Maine also revealed a low percentage of immature birds, 

 i.e., 11% in 1962 (Sprunt 1963), 21% in 1963 (Sprunt and Ligas 1964), and 

 14% in 1975 (Cammack 1975). Data computed over a period of years, 1961 to 

 1977 (Christmas Bird Counts) and 1963 to 1978 (Midwinter Waterfowl/Eagle 

 Inventories), indicate only 21% immature eagles in Maine's wintering eagle 

 population. 



The age ratio is biased against immature eagles because their relatively 

 inconspicuous plumage makes them less visible to surveyors. Poor reproductive 

 success in Maine's breeding eagle population also contributes to low 

 percentages of immature eagles. Age ratios of wintering eagles in the Pacific 

 Northwest indicate a range of 35% to 52% immature individuals (Hancock 1964; 

 Servheen 1975; and Stalmaster 1976). The latter figures probably reflect 

 greater recruitment among eagles nesting in the Pacific Northwest. 



Maine's midwinter eagle population is widely dispersed. The absence of large 

 winter concentrations possibly reflects a lack of locally abundant foods which 

 could result in a scarcity of immatures whose foraging skills are not well 

 developed. 



Migration . No data are available on migration of adult bald eagles from 

 Maine. Only 16 immature eagles among those banded as nestlings in Maine have 

 been relocated after fledging. Seven first-year, one second-year, and one 

 third-year bird were found within 90 miles (145 km) of their natal nests in 

 the State. Three others were seen during their first fall or winter in Maine 

 and two wintered in Massachusetts. A two-year-old eaglet was relocated 220 

 miles (355 km) away in New Brunswick. The only documented case of dispersal 

 out of the northeast was a juvenile observed in South Carolina, having 

 traveled over 930 miles (1500 km) within 4 months of fledging in Maine. 



Adult eagles were observed on 1977 to 1979 midwinter surveys at 20 coastal 

 nest sites that had been occupied the previous breeding season. At least 45% 

 of the breeding sites in the characterization area known to be inhabited 

 during the 1976 to 1978 breeding seasons also were occupied in winter. Many 

 pairs nesting on the coast remain on breeding territory throughout the year. 

 However, winter ranges are flexible and change to meet the food supply. 

 Fidelity to nests by wintering eagles supports the belief that much of the 

 eagle population nesting in Maine also winters in the State. 



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